Conventionally, the C/N ratio of a signal provided from a DUT (Device Under Test) has been measured, and a system configuration for the measuring is shown in FIG. 7.
The frequency of a signal Fs provided from a DUT 102 is multiplied by about a few tens by a multiplier 104. The frequency of a signal Fs×N provided from the multiplier 104 is reduced by a down converter 106 down to a frequency which a digitizer 108 can process, and then, the signal is supplied for the digitizer 108. The digitizer 108 can measure the C/N ratio of the signal Fs×N provided from the multiplier 104. Note that since the C/N ratio is reduced by multiplying the frequency of the signal Fs provided from the DUT 102, the reduced amount is obtained by calculation, and the C/N ratio of the signal Fs provided from the DUT 102 is obtained.
Alternately, the measuring system may be configured as shown in FIG. 8. Though this system is identical to the example above up to the process where the signal provided from the DUT 102 is multiplied by about a few tens by the multiplier 104, the frequency of the signal provided from the multiplier 104 is not reduced, and is processed by a spectrum analyzer 110. The C/N ratio of the signal Fs×N provided from the multiplier 104 can be measured by the spectrum analyzer 110. Note that since the C/N ratio is reduced by multiplying the frequency of the signal Fs provided from the DUT 102, the reduced amount is obtained by calculation, and then, the C/N ratio of the signal Fs provided from the DUT 102 is obtained.
However, since the frequency which the digitizer 108 can handle is generally about a few tens of MHz, the down converter 106 is necessary in the system shown in FIG. 7. The down converter 106 which meets such a high frequency signal as supplied from the multiplier 104 is expensive, and its circuit is complex.
In the system shown in FIG. 8, since the processing speed of the spectrum analyzer 110 itself is generally slow, the overall processing speed also is slow.
In view of the foregoing, the present invention has a purpose of providing an apparatus and the like which can measure the C/N ratio provided from the DUT at a high speed or with a simple constitution.